Radio-frequency–based drone classification is a critical capability for modern antidrone systems. However, the development of dependable artificial intelligence models in this domain is hindered by the high cost and complexity of expert data labeling. This challenge is particularly pronounced in radio-frequency signal analysis, where labeled datasets are typically small, partially unlabeled, and continuously evolving during system deployment. This paper proposes a tailored active learning framework for drone classification in the radio-frequency domain, integrating human expertise into an iterative learning process that selectively queries the most informative unlabeled samples. By prioritizing sample informativeness, the proposed framework aims to achieve high detection performance while significantly reducing labeling effort. Theapproach is evaluated using the VTI_USRP_DroneSET dataset, comprising radio-frequency spectrograms acquired in realistic outdoor conditions within the 2.4 GHz frequency band. Experimental results demonstrate that the proposed active learning strategy achieves mAP50–95 performance comparable to conventional supervised learning while requiring only one quarter of the labeled data. The results confirm that active learning enables data-efficient radio-frequency based drone classification without compromising detection accuracy. Furthermore, near-optimal performance is consistently obtained with an optimal training duration of 80 epochs, reducing both annotation and computational costs. These findings confirm that active learning provides a data-efficient and cost-effective solution for RF-based drone classification and is well suited for real-time deployment in operational antidrone systems where labeled data are scarce and continuously acquired.
The aim of this work was to establish an empirical correlation between strength, hardness and electrical conductivity, i.e. mechanical and physical properties of the EN AW-7075 alloy during the natural ageing. The results indicate a good correlation between hardness/strength and electrical conductivity. It was found that the correlation between 0.2% proof strength (R p0.2) and tensile strength (R m) with hardness (HB) and electrical conductivity, as well as hardness with electrical conductivity, exhibit a nonlinear dependence, with the coefficient of determination, R², between 0.9618 and 1. These relationships can be used for monitoring the ageing and predict the strength by nondestructive testing.
Constant development of protective materials and armored systems requires continuous improvements in the field of anti-tank ammunition development. One of the most commonly used anti-tank explosive ordnance are shaped charge projectiles/warheads. Serbia has been globally recognized for decades in the production of high-quality hand-held rocket launchers equipped with various calibers of shaped charge ammunition. One of the most famous representatives is the 64 mm hand-held rocket launcher, better known as “Zolja“. Although it has been in use for decades and it has insufficient capabilities against more modern protection systems, retaining the traditional design and long-established production technologies, along with the use of more potent and modern explosives, could significantly enhance its penetration power. This paper uses analytical calculation and numerical simulation to analyze how different explosive materials affect the velocity of shaped charge jet of 64 mm M80 warhead, which ultimately directly impacts its penetration capabilities.
The paper presents research conducted on the current VSS Vintorez rifle and the concept of an improved modular weapon system on the AM20 platform with a subsonic system of ammunition 9×39 mm. The test was conducted with the aim of comparing the characteristics of the weapon required for special tasks. The determination of the characteristics of the existing weapon and the concept of an improved modular system on the AM20 platform was carried out through experimental tests. The test was conducted to compare the accuracy and precision of the weapon with a subsonic ammunition system with a 9×39 mm bullet. The tested automatic weapon systems were realized at 100 m under standard conditions, with the appropriate number of shots (ten groups of ten shots each with identical ammunition). The emphasis during the testing was on measuring the muzzle velocity, accuracy, and precision, according to standard testing methods. The results of experimental tests showed a high level of accuracy and precision and an adequate level of initial velocity values. Based on the conducted comparative analysis of accuracy and precision, the possibilities of use in the implementation of tactical tasks in urban environments for the proposed concept of an improved modular system on the AM20 platform were given.
This paper presents the development, structural and mechanical characterization of composite thin-walled tubes (CF/GF/UPe) based on a polyester resin matrix, reinforced with carbon (CF) and glass fibers (GF). The tubes were fabricated using wet filament winding technology, which offers precise control over fiber orientation. The manufacturing process involved two distinct winding patterns: radial and helicoidal, to assess their effects on the mechanical performance of the tubes. Detailed experiments were conducted to evaluate the influence of the winding angle (radial vs. helical) on the internal hydrostatic pressure. It was observed that the helicoidal winding pattern, particularly at a winding angle of 70°, significantly enhanced the response of the CF/GF/UPe tubes on internal hydrostatic pressure. The findings provide valuable insights into the design and fabrication of composite tubes for applications requiring high strength-to-weight ratios, such as in automotive, aerospace, and structural engineering fields. The research offers a comprehensive understanding of the relationship between filament winding parameters especially winding angle, and the mechanical performance (Barcol hardness and response of the material to internal hydrostatic pressure) of novel composite thin-walled tubes, providing a basis for future optimization in the production of fiber-reinforced composite tubes.
